Assessment of pesticide and heavy metal residues in tilapia fish from Machakos and Kiambu counties, Kenya

Abstract

Exposure to pesticides, heavy metals and other chemical residues cause harmful effects; they can cause injury to human health as well as to the environment. Humans take up these chemicals through skin absorption, respiration and ingestion of contaminated food. Among all foods, fish is one of the main sources of chemical contaminants although fish products account only for about 10% of diet or less. The present study was conducted in Kiambu and Machakos counties with objectives of determining the concentration levels of pesticides and heavy metals in edible parts of fish from inland fish farms, The dietary intake of pesticide and heavy metal was also estimated and compared with acceptable daily intakes of the World Health Organization (WHO) guidelines so as to assess their potential health hazard. A total of two hundred and thirty tilapia fish samples (n= 230) were collected from Kiambu and Machakos counties in the months of September and October 2011. Following wet digestion, the levels of lead and cadmium were determined in muscle, liver, gonad and brain of tilapia fish using Atomic Absorption Spectrophotometer (AAS) fitted with cadmium and lead lamps set at their respective wavelengths. To evaluate organochlorine concentration, fish samples were extracted, cleaned and analyzed using Gas Liquid Chromatography (GLC) fitted with Electron Capture Detector (ECD). The data was subjected to descriptive statistics and Analysis of Variance (ANOVA) to test levels of significance at 95% confidence limit using Statistical Analysis Software (SAS) 9.0 version. Significance was noted at P< 0.005. In Kiambu county, mean lead levels (x ± s.d) in brain, liver, gonad and muscle were 31.31 ± 28.27, 17.33 ± 20.64, 16.62 ± 15.42 and 3.78 ± 2.22 ppm respectively against `the benchmark value of 0.5ppm.The average cadmium levels (x ± s.d) in the brain, liver, gonad and muscle were 7.25± 6.59, 5.35 ± 6.12, 3.35 ± 4.16 and 1.66 ± 2.48 ppm respectively against the benchmark level of 0.05ppm.However, only positive samples were considered. Out of the total number of samples analyzed, only 40% were positive for lead and cadmium in Kiambu county and 34 % in Machakos County. In Machakos county, mean lead levels (x ± s.d) in the brain, liver, gonad and muscle were 30.40±20.56, 7.88 ±7.25, 13.29±14.28 and 12.22±22.96 ppm respectively against the benchmark level of 0.5ppm.The average cadmium levels (x ± s.d) were 3.91±5.84, 2.90±3.58, 1.25±1.38 and 1.12±1.13ppm respectively against the benchmark level of 0.05ppm. The Organochlorines exhibiting the highest concentration (x ± s.d) were o,p ‘-DDT with a mean of 2.098±4.097 μg Kg-1 followed by p’p-DDD 1.684±3.666 μg Kg-1 in the brain tissues. This was followed by p’p-DDD in muscle at 0.916±1.287 μg Kg-1 and pp-DDT at 0.916±1.916 μg Kg-1. Machakos County had p,p’-DDT at a concentration of 0.158 μg Kg-1 ,p,p’-DDD had 0.097 μg Kg-1 and p’-DDT had a concentration of 0.016±0.016 . Statistically, there was no significant difference in the tissues analyzed for the concentration of Pb in the two counties since pr/t/>0.05. Cadmium concentration in the gonad had a significant difference between Kiambu and Machakos County since pr/t/=0.05.The brain, liver and muscle did not show any significant difference in the concentration of Cadmium between the two counties since pr/t/ >0.05 . The results of the current study indicate the presence of relatively high levels of lead and cadmium above permissible limits in fish from the study areas and recommend controlling industrial and agriculture effluents into surface water and proper sitting of ponds to minimize the risk of contamination of farmed fish by pesticides and heavy metal. However it was noted that the number of samples that were positive with regard to the presence of all residues was small compared to the total number of samples analyzed.